Young women in sub-Saharan Africa are at incredibly high risk of HIV infection; 76% of all new infections among young people occur in young women and 77% of HIV positive women globally live in sub-Saharan Africa. Given this, young women have been prioritized as a key population in need of urgent prevention interventions. However, there is a paucity of longitudinal data to understand the multiple levels of social, community, household, and individual factors that shape HIV incidence among young women in sub-Saharan Africa. To date, much of the data on HIV risk in young women has focused on individual-level factors; in particular sexual behavior, has been cross-sectional in nature and often has lacked rich information on social determinants which are key to shaping young women's HIV risk. The overall objective of this application is to determine the effect and mechanisms of effect of key social determinants measured at multiple levels (e.g., individual, household, and community) that influence HIV acquisition in young women in South Africa. In this application, we focus on three under-examined thematic areas which cross-cut multiple levels of influence and that our research and the literature suggest are critical to shaping young women's HIV risk-gender inequity, schooling and socio-economic status, and emotional well-being. Understanding how these determinants shape risk and protection is critical to developing effective interventions to reduce new HIV infection. We have established an ongoing cohort of 2,500 adolescent South African girls, followed through key life transitions into early adulthood; notably this data includes HIV incidence and many key determinants of HIV infection including important life transitions such as coital debut and school completion at multiple time-points. In this application, we propose one additional data collection point as the cohort is entering a period of high HIV incidence. Uniquely, we can link our cohort data with two rich data sets that contain community social environment data as well as population demographic surveillance (census) data. Using the data collected from our longitudinal cohort of young women combined with comprehensive demographic surveillance data and community-level context data, we have a unique opportunity to triangulate and leverage NIH-supported research in order to understand how key social determinants shape HIV risk in young women in South Africa as they transition from adolescence into young adulthood. We also will quantify how intervening on these key social determinants, separately and in combinations, could impact HIV incidence in young women providing critically needed insights for prevention programs targeting this population.